Series & Parallel Resistor Calculator
Enter 2 or 3 resistor values, pick series or parallel, and click Solve — watch them merge into the single equivalent resistor.
Enter resistor values and click Solve.
Formula & edge cases
Parallel: 1/Req = 1/R1 + 1/R2 (+ 1/R3)
1Worked example (parallel): 100Ω & 100Ω → 1/Req = 1/100 + 1/100 = 1/50 → Req = 50Ω. Two equal resistors in parallel always halve.
Common questions
Why does parallel resistance always come out smaller?
Adding a parallel path gives current more ways to flow, which always lowers total resistance — the equivalent is always smaller than the smallest individual resistor in the combination.
Why does series resistance always come out bigger?
Series resistors force current through each one in turn, so their resistances simply add — the equivalent is always bigger than the largest individual resistor.
What if I have more than 3 resistors?
Combine them in pairs: solve the first two, then treat that result as one resistor and combine it with the third, and so on. The series and parallel formulas both extend this way for any number of resistors.